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Giant Wimshurst Machine - could use some guidance

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Antonio

Thu Jun 26 2014, 11:58PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

You are using fiber brushes in the neutralizers, right? They may cause startup problems due to the high resistance. Use thin metal wires in at least one of the brushes. Try also to excite the machine by placing an electrized PVC tube opposite to one of the neutralizer brushes.

AwesomeMatt

Fri Jun 27 2014, 02:17AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

wrote ...
If you can, reduce the separation between the discs.

Not easily done. My spacers are fixed and I have to cut new lengths every time, and I have to have help pulling it apart.

BUT.. they're probably too far apart anyway, so, it was on my list.

Issues with bringing them closer together are the fact that the axle is already bowing (so discs are closer at the top than the bottom), and one of them is still wobbley so it needs some separation. I can probably reduce it by half though.

wrote ...
Also, make sure that when a sector is under a neutralizer brush, that it is aligned with a sector on the opposite disc.

... Hrm.

On the opposite disc, or the opposite side of the same disc?

The latter... making sure the neutralizer bars short sectors on each side... done.

The former... I'm not sure I understand correctly.

Let's take one disc and neutralizer bar as fixed. How should the one on the opposite side be arranged at that particular snapshot in time? Where the neutralizer brush touches the sector on the front disc, the rear disc should be what? Also a sector? And the opposing neutralizer brush also there?

Previously... the neutralizer brushes were not matched. One was more vertical than the other. It still worked immediately.

Also... the belts are now stretched, so, discs don't spin in lock step. Generally one or the other starts to spin first. The belts slip and they stretch too so there's no way to ensure what's happening on one side is happening on the other.

wrote ...
Any chance that the backsides of the discs have become dusty?

Two weeks in a shop that does mostly woodworking? Yep.

Not that dusty, but, dusty, sure. Also, I only alcohol wiped the sector covered parts.

Add that to my regular maintenance suggestions?

wrote ...
You are using fiber brushes in the neutralizers, right? They may cause startup problems due to the high resistance.

Yes, carbon fiber. I didn't measure the resistance.. I should do that. Maybe the ozone degraded the brushes or something.

wrote ...
Use thin metal wires in at least one of the brushes.

Okay, will do.

wrote ...
Try also to excite the machine by placing an electrized PVC tube opposite to one of the neutralizer brushes.

Just give a tube of PVC a silk rub, or do I need to create a steady electrical source?

...

The thing that is shocking is that, it's not just not working a little bit, or seeing a performance decrease. It's right dead nothing at all.

Antonio

Fri Jun 27 2014, 02:45AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Excessive distance between the disks may be a problem, but if the machine was working before in the same condition the distance is ok. Axle bowing is a big problem. You may need to use a stronger axle. To excite the machine a well electrized PVC tube shall be enough. Verify if the humidity is low. Heat the disks and insulators a bit with a hair dryer if it is high. Aligning the neutralizers is not necessary, but good if they are insulated from the structure of the machine.

AwesomeMatt

Fri Jun 27 2014, 03:24AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

wrote ...
Aligning the neutralizers is not necessary, but good if they are insulated from the structure of the machine.

They are definitely not insulated, can't figure out a way for them to be insulated, since they have to be mounted to it. They effectively short to the axle and the support beam.

-----

In other news, I would really like to give back to the community by documenting this build and creating a tutorial on how to design a machine of any size.

There is really no place that has this knowledge recorded anywhere. I would have been way in over my head without one-on-one mentoring, interaction, and Q&As from 4HV and other places.

Once the show and tell from this machine is complete, I would like to use this thread to learn more about how and why some of the constraints in the machine are what they are. I have tried to learn as much as I could so I can solve my own problems, but I know at least half the time I just took someone's answer, or number, and used it blindly without having any context behind it. That worked for me, but it's very prescribed.

My goal would be to make a tutorial that takes something complicated, and explains how someone with almost no knowledge of electronics or physics could solve their own problems when designing a machine.

So, hopefully I can continue to pick your guys' brains a bit more, and then after that whenever anyone asks those questions you can say "One of our members filmed a tutorial, just go watch that" instead of explaining it again or giving them specific numbers that work only for that specific person.

kilovolt

Fri Jun 27 2014, 09:36AM

Registered Member #2018 Joined: Tue Mar 10 2009, 09:56AM
Location: Switzerland
Posts: 74

AwesomeMatt:
I would highly recommend to replace the fiber brushes with something with really low resistance. I had exactly the same problem with one of my selfmade machines (I took brushes from a laser printer). Sometimes it worked, but sometimes the machine didn't start at all. Take copper brushes and it will work again (I know the copper brushes will lead to scratched disks, but with these the machine will work reliable).

I tried several other materials for the brushes, for example some sort of an antistatic packing material, which had the same results: Intermittent starting problems.

Humidity has an influence, but even with relatively high humidity my machines work, however with less output of course.

Good luck
kilovolt

Dr. Slack

Fri Jun 27 2014, 09:43AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The crossed neutraliser bars. If they are ungrounded, then they *must* touch opposite segments at the same time. If they are grounded (and the wood frame may or may not be an adequate ground at these voltages and currents, it all depends on humidity and wood type, use a wire to be sure) then that requirement disappears. All they need to do is to ground the top surface of a segment as it passes opposite the charged segments on the other disk. This is how the charging mechanism works. Look up induction charging, for instance

, the Wimshurst machine automates this process by passing the segment close to the segments on the other disc, grounding it briefly (or connecting it to the oppositely charging segment which amounts to the same thing), and then pulling it away again. Another way to look at it is the neutraliser contact just has to source or sink whatever charge has to flow to the segment. That means it either needs a connection to ground, to the other oppositely charging segment, or has to have a large capacitance to ground.

There's no requirement to phase the segments on one disc to the other disc *assuming* the discs are further apart than the gaps between the segments, and the segments are wider than the gaps. That is, each segment when it's under the neutraliser bar being charged just has to see 'some charge' on the opposite disc.

Is the machine still not working? Any leakage from the segments or the output terminals will kill it. Get a fan heater / hair drier / paint stripper and make sure the machine is dry on the surfaces. Can the room's AC be adjusted to be drier? I've seen many an electrostatic demo that didn't work until everything had been dried out.

If that fails, test all parts of the machine for their ability to hold a charge. Ideally, build or buy an electroscope, ye-olde fashioned hanging V-shaped gold-leaf thingy. And you could do with a source of high voltage, can you borrow a small VandeGraff or Wimshurst from anywhere. Charge up each output terminal, see if they hold charge. If not, separate the terminal and Leyden jar, and test each separately. You could check the segments, but really if you've alcohol wiped the discs then there's not a lot more you can do.

A great place to document the how of the machine would be on our HVwiki. You might even get some others pitching in to add and fix stuff.

AwesomeMatt

Fri Jun 27 2014, 10:25PM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

I tried charging it with a big staticy PVC tube that I'd rubbed on my shirt until it crackled. I'm not sure how to charge it. Homemade Lightning is a bit contradictory. Neutralizer bars form an X... I'm supposed to hold it behind one neutralizer bar, where there is no bar on the back side? Hrm.

I held it all over the place.

Not any effect that I could tell.

I did notice that the belts are so stretched they now fit over the 12" pulleys.. so I figured, why not, and stretched them over the big pulleys. Lo and behold.. when I got it going REAAAAALLY fast, snap crackle pop SPARK. But it has to be moving really, really, fast to get anything. Like there's a critical mass.

Two weeks ago, I hardly had to get it going at all before it was farting electricity.

Also... when I get it going that fast it's rocking and swaying a lot, so, I don't want to neglect the possibility that the machine is working simply because of some benevolent unballancing issue that corrects the problem.

I'm kinda heartbroken about the carbon fiber being a bum choice, but, if it is then it is. I'll go looking for brass instead again.

The neutralizer bars are copper, sitting directly on the upper metal axle, so, they're certainly grounded to each other. But they aren't now and have not ever been symetrically angled to each other.

Since the brushes only touch the last 1/2" of sector, and it's rounded... there's a good chance there will be dead spots on the reverse side.

I first joined 4Hv a couple years ago to add to the wiki, but, it seems functionally abandoned. I don't mind documenting things, but I loathe documenting things that no one reads or participates in.

...

Up next... trying out these Leyden jars while spinning really really fast.

Eleccentric

Fri Jun 27 2014, 11:29PM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

You could probably salvage some very thin and springy flat metal from an old wind-up watch or an analog movement meter.

I wouldn't abandon the carbon fiber entirely - perhaps more substantial brushes made from longer sections of tow would work better.

Antonio

Fri Jun 27 2014, 11:53PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

If the machine works only at high speed the most probable problem is leakage. Verify if the insulators holding the charge collectors are clean and dry. Verify if the machine works without the charge collectors. With only the neutralizers in place it shall charge the disks very evidently.
Look also at possible points in the charge collector assembly that may be causing leakage. A speckle of dust in the wrong place is enough. I like to clean these machines with furniture cleaning products containing silicone and wax, instead of with alcohol. WD-40 works too. Test any cleaning product first in a section of pvc tube, that must be easily electrizable by friction after cleaned. As a last resource, decrease the separation of the disks.

Eleccentric

Sat Jun 28 2014, 12:53AM

Registered Member #33460 Joined: Tue Aug 27 2013, 06:23PM
Location: Seattle
Posts: 46

Sooner than use brass, beryllium copper or phosphor bronze would be much better choices.

Or perhaps you could use bunches of tiny steel ball bearings, or just iron filings, attached to very strong NIB magnets. I'd be wary of the filings since they might get picked off by strong electric charge.

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